Generally, stereo signals are generated and used most frequently and widely by consumers. Recently, multi-channel signals tend to be popularly used. Yet, limitation is put on mix signals which are processed not by a source signal unit but by a channel signal unit. So, in case of processing a mix signal by a channel signal unit, it is unable to independently process a specific source signal configuring the mix signal. For instance, it is impossible to raise a volume of background music only while a volume for actors' voices is maintained uniform in viewing a movie.
Moreover, in order to independently process and remix a mix signal (or synthetic object signal) per a source, i.e., per a specific source signal, a user has to raise or lower a volume level per a source signal (or mute a sound by setting a level to zero) or adjust a relative position of a source signal.